This invention relates to the preparation of biological
Prior Art
Heretofore smears of biological substances such as blood or cellular suspensions have been prepared for microscope examination by manipulation of microscope slides and slide cover slips. The technique requires a certain degree of expertise and, even with such skill, resulting smears have tended to lack uniformity and reproducibility. In the common manual preparation technique in which an end edge of an elongated slide is drawn lengthwise along a plastic strip or another such slide to smear a droplet of blood on the last-mentioned slide, the heavier cellular material tends very strongly to move out or away from the central longitudinal portion of the smear to be left on the smear in congregations along the sides of the smear. This is undesirable for microscopic cell examination. For such examination it is desirable that the cellular distribution be substantially even across the width of the smear throughout any given portion of the smear length. On the other hand, while it is desirable to have a monolayer portion of cellular material available for such examination, it is also desirable to have available on a portion of the same smear a cellular gradient extending lengthwise of this smear and effecting some overlapping of cellular material in such region. Such smears having both types of layers permit differential cell counts under a microscope which counts are useful for diagnostic purposes, such as for malarial diseases for example.
It has been proposed that smears be prepared by a spinning process, and apparatus for carrying out such process has been commercially available. The process is one of centrifuging on a microscope slide a volume of biological fluid such as blood for a period sufficient to spread the specimen over a portion of the slide. It has been indicated in connection with such spinners that virtually the entire resulting smear has a mono-layer cellular distribution. This may be a drawback as previously indicated. Another drawback in such use of spinners is that an excess of a liquid specimen such as blood is spun off the slide to spray the environment such as ambient air and also splatter the inner wall surface of the spinner. Such blood specimens may carry infectious diseases, and hence the required cleanup operation of such spinners after use may be hazardous.
It is desired to obviate the aforementioned problems in the preparation of smears of biological substances. Moreover, it is desired to provide a method and apparatus for a preparation of such smears, which may be readily automated.